You need to make sure you are using JDK 5.0 when running JBoss for EJB3. This is because the EJB3 spec uses JDK 5.0-only features such as generics, annotations and Enums. The EJB3Deployer has been compiled w/ JDK 5.0, and that the error you are seeing means that you are trying to run it with JDK 1.4.2